Copolyetheresters are well known and have enjoyed continued and increasing commercial success. They are available from several sources including Hytrel.RTM. resins from E. I. duPont and the RITEFLEX resins from Celanese (formerly GAFLEX from GAF) and are described in U.S. Pat. Nos. 3,023,192; 3,651,014; 3,763,109; 3,766,146; 3,784,520; 3,801,547; 4,156,774; 4,264,761 and 4,355,155, among others. These copolyetheresters have a number of desirable properties including excellent tear strength, flex life, toughness, and general elastomeric stress-strain characteristics.
It has been found that polyetheresters can be improved or enhanced for certain applications, especially with respect to improving the "softness" (i.e., lower durometer) of the elastomer, while retaining satisfactory tensile properties.
The improvements are accomplished by the incorporation of effective amounts of certain rubber modifiers of the type known as multistage interpolymers. It is surprising, however, that elastomeric compositions incorporating the selected rubber modifiers can be processed to avoid the delamination or phase separation (or so-called "cheesiness") expected for the combination of thermoplastic elastomers and typical rubber products.
In particular it has been found that copolyetherester elastomers can be improved by incorporation of effective amounts of rubber modifiers characterized as a multi-stage, or sequentially produced interpolymer product, specifically a thermoplastic elastomer comprised of a crosslinked polyacrylate rubbery phase which is interpenetrated by a crosslinked styrenic phase. This multistage interpolymer elastomer has been added to thermoplastic resins. See, for example, above mentioned U.S. patent application Ser. No. 152,524 filed Feb. 5, 1988.
It has now been surprisingly found that effective amounts of the aforementioned multistage polymer modifier can be combined with a copolyetherester and the elastomeric product will thereupon exhibit improved "softness" while retaining satisfactory tensile properties.
It is an object of the present invention to provide thermoplastic elastomeric molding compositions which are suitable for a broad range of end use applications having sufficient flexural modulus so as to provide molded parts with good physical integrity and stiffness.